Two major environmental groups announced an alliance Monday between their political action arms in an effort to expand their influence on national policymakers.

The League of Conservation Voters and the Natural Resources Defense Council Action Fund are starting LeadingGreen, a collaboration that will steer donations to federal candidates and enlist the help of major donors in lobbying elected officials. Although the move was not prompted by the Supreme Court’s decision this month to strike down the overall limit on how much individuals can give candidates and political parties, LCV President Gene Karpinski said the ruling highlights what has motivated the groups.

“It underscores the fact we need more environmental money in politics, and we need more environmental donors doing advocacy to make sure politicians understand they feel strongly about these issues, and that’s what the new alliance is all about,” Karpinski said in an interview.

The LCV’s political action committee raised and contributed $2 million to candidates during the past election cycle; the NRDC Action Fund primarily operated by encouraging its donors to give directly to candidates or environmental advocacy groups, and it established a political action committee last year. The new initiative aims to raise and contribute $5 million directly to candidates this year, according to officials, separate from independent expenditure spending activities.

That sum is more modest than what many conservative groups will spend on the election, as well as below the $100 million that billionaire and climate activist Tom Steyer has pledged to mobilize by 2016. NRDC Action Fund President Frances Beinecke described the two ventures — which will both highlight climate change — as “parallel efforts.”

“We certainly welcome what Tom’s doing. He’s able to go to a scale that we’ll hopefully get to one day,” she said, adding that the new coalition will be “principally focused on the Senate, the president’s climate action plan and, in particular, the power-plants rule. That’s the number-one priority in this cycle.”

The NRDC has traditionally focused on policy and legal advocacy; the LCV has concentrated on federal and state elections. Democrats and their environmental allies lack the votes in Congress to pass the kind of broad climate bill that the House adopted in 2009, but they are working to ensure that Republicans do not make such major gains this fall that they could block the president from using his executive authority to regulate greenhouse-gas emissions.

Business groups started a multimillion-dollar campaign in January criticizing the Obama administration for its climate rules, including those that would limit carbon-dioxide emissions from power plants. That coalition includes the American Farm Bureau, the National Association of Manufacturers, the U.S. Chamber of Commerce and 75 other groups.

Americans for Prosperity spokesman Levi Russell, whose group has received financial support from Charles and David Koch, wrote in an email that he was skeptical that environmentalists will be able to persuade lawmakers to take a more aggressive stance on carbon regulation.

“There’s a good reason why any legislation based on environmental ideology has come to a grinding halt in Congress. Most Americans are far more concerned about jobs, the economy and the impact of Obamacare,” wrote Russell, whose group has focused on the health-care law this year but recently ran an ad attacking Sen. Mark Begich, D-Alaska, for his position on carbon pricing. “Policies based on shaky data that result in higher energy prices will be a pretty tough sell.”

However, Carol Browner, who served as Obama’s special assistant on energy and climate change during his first term and now chairs the LCV’s Board of Directors, wrote in an email, “LeadingGreen is uniquely situated to help shift the politics of climate change in Congress in order to make the progress we so desperately need.”

Daniel Tishman, chairman of the NRDC’s Board of Trustees and a major real estate developer and donor to environmental groups, said contributors such as himself “more and more these days are looking for outcomes,” and having a measurable impact on campaigns will sway elected officials because they “read the tea leaves.”

“Our strategy is, at the end of the day, to really keep electeds at every level accountable for what they do,” Tishman said.

Sen. Edward Markey, D-Mass., who received support for his 2013 Senate bid from the LCV and Steyer’s NextGen Climate Action Committee, said in a phone interview Sunday that he and other elected officials will need environmentalists to become more politically active in order to stay in office.

“The polluters are sparing no expense to defeat supporters of clean energy, climate change and environmental protection,” he said. “There’s no way to compete against these polluted dollars without significant help from environmentalists.”